O6-Methyguanine-DNA Methyl Transferase (MGMT) Promoter Methylation in Serum DNA of Iranian Patients with Colorectal Cancer

Abstract

Introduction: Colorectal cancer (CRC) is a leading cause of cancer deaths worldwide but current molecular targeted<br />therapy is not providing major success in CRC treatment, so early detection by non-invasive methods continues to<br />be vital. Aberrant methylation of CpG islands in promoter regions is associated with inactivation of various tumor<br />suppressor genes. O6-methyguanine-DNA methyltransferase (MGMT) is a DNA repair enzyme that removes mutagenic<br />and cytotoxic adducts from O6-guanine in DNA. Aberrant hypermethylation of the MGMT promoter has been<br />associated with lack of mRNA expression, with concomitant loss of protein content and enzyme activity. AIM: Our<br />aim was to determine whether MGMT promoter methylation might be detectable in circulating free DNA in the serum<br />of CRC patients and normal individuals using a methylation specific (MSP) polymerase chain reaction (PCR) method.<br />Methods: A total of 70 subjects were enrolled in the study. Of these, 30 patients who were diagnosed previously as<br />untreated colon adenocarcinoma by a gastroenterologist and the other 40 were nearly age-matched individuals who had<br />a normal colonoscopic evaluation (except for hemorrhoids or fissures) and normal pathologic reports. After bisulphite<br />modification of DNA, serum samples were examined for MGMT promoter methylation using MSP. Results: Ninety<br />percent of CRC patients had MGMT promoter hypermethylation as compared to no methylation in normal subjects'<br />serum. Most of the cancers were stage П and moderately differentiated adenocarcinomas; nearly 60% were found in<br />the left colon. No statistically significant correlation was found between the promoter methylation status and gender<br />and age. Discussion and Conclusions: MGMT hypermethylation can be detected in free circulating DNA in serum of<br />CRC patients and can be used “as a clinical biomarker" for early diagnosis and prognostic assessment of the disease.<br />Our data confirm previous studies indicating utility for free circulating DNA as a serum biomarker for early detection,<br />diagnosis and monitoring of CRC patients.